Ruthenium-based catalyst for producing lower polyhydric alcohols

ABSTRACT

A ruthenium-based hydrogenation catalyst, particularly but not exclusively for hydrogenolysis under pressure of higher polyhydric alcohols, comprises ruthenium supported on granular activated carbon, and has: 
     a specific surface area of from 600 to 1000 m 2 /g; 
     a total pore volume of from 0.5 to 1.2 cm 3 /g; 
     an apparent specific weight (bulk density) of from 0.45 to 0.55 g/cm 3 ; 
     an actual specific weight of from 1.9 to 2.3 g/cm 3 ; 
     a total volume of micropores having a radius smaller than 75 A of from 0.4 to 0.55 cm 3 /g; and 
     an ash content of from 2 to 5% by weight. 
     The catalyst is used in a method for the continuous production of lower polyhydric alcohols in a fixed bed reactor, by means of hydrogenolysis under pressure of higher polyhydric alcohols.

The present invention relates to a method for production in a fixed bedreactor of lower polyhydric alcohols and their mixtures, comprisinghydrogenolysis under pressure of higher polyhydric alcohols in thepresence of a supported metal catalyst.

In the present description, the term higher polyhydric alcohols meansproducts such as sorbitol, mannitol and xylitol derived from catalytichydrogenation of carbohydrates (and in particular of glucose, fructoseand their mixtures). The term lower polyhydric alcohols meanspolyalcohols having a maximum of 6 carbon atoms and a maximum of 3hydroxyl groups, in particular ethanediol, propylene glycol, butanedioland glycerol.

The invention also relates to a new supported ruthenium-based catalystand its use in the production of chemicals from renewable raw materials(carbohydrates and their derivatives); in particular for selectivetransformation of low molecular weight polyhydric alcohol hexoses.

U.S. Pat. Nos. 2,868,847 and 4,476,331 describe the use of aruthenium-based catalyst on a powdered active carbon support. Themethods of hydrogenation and catalytic hydrogenolysis described in thesedocuments comprise batch reactions in which the powdered catalyst issupplied to the reactor together with the reagents.

A first object of the present invention is to provide a method of thetype specified initially in the description, which enableshydrogenolysis of higher polyhydric alcohols to take place in acontinuous fixed bed reactor.

For this purpose, a second aspect of the invention consists of use of aruthenium-based catalyst supported on granulated activated carbon,having:

a specific surface area of 600 to 1000 m²/g (B.E.T. method);

a total pore volume of 0.5 to 1.2 cm³/g (combined nitrogen-mercurymethod);

an apparent specific weight (bulk density) of 0.45 to 0.55 g/cm³;

an actual specific weight of 1.9 to 2.3 g/cm³;

a total volume of micropores having a radius smaller than 75 A of 0.4 to0.55 cm³/g; and

an ash content of 2 to 5 weight %.

The specific type of activated carbon used having the aforementionedfeatures also has high mechanical resistance and a particle size whichmake it suitable for use in a fixed reactor of the trickle-bed type.

The possibility of being able to carry out fixed bedhydrogenation/hydrogenolysis enables increased productivity of the plantto be obtained. It has also been found unexpectedly that fixed bedhydrogenolysis enables increased selectivity of lower polyhydricalcohols to be obtained in comparison with a reaction in batch form.

The specific surface area of the granulated activated carbon support ispreferably between 800 and 1000 m²/g, and the total volume of the poresis between 0.6 and 0.7 cm³/g.

By granulated activated carbon is meant a carbon which has a particlesize of between 5.7 and 0.5 mm (3 and 32 mesh) and preferably a particlesize of between 4.7 and 2.4 mm (4 and 8 mesh, Tiller series). Theoptimum particle size is selected on the basis of the processparameters, according to known criteria.

Use of activated carbon which has the above-described characteristics iscritical for the purposes of the activity of the catalyst and thepossibility of using it on a fixed bed.

Activated carbon of the aforementioned type is available commercially inthe form of the activated carbons made by ACQUE NYMCO having thereferences GH12132 and CA12132.

In the hydrogenolysis method according to the invention, the reactiontemperature is generally between 200° and 300° C., and preferably 220°-270° C., the spatial hourly velocity of the fluid is between 0.3 and 4,and preferably between 0.67 and 2.50 h⁻¹, and the reaction pressure isbetween 5 and 20 MPa and preferably between 7.5 and 15 MPa. Thecontinuous reactor is preferably supplied with a reaction promoterselected from amongst alkaline and alkaline earth hydroxides, andpreferably sodium hydroxide, or basic reaction salts; the molar ratiobetween the higher polyhydric alcohols and the promoter supplied isbetween 3 and 30. The reactor is preferably also supplied with sulphidesas reaction moderators (in order to avoid the formation of undesirablefinal products such as methane), with a concentration in the solutionsupplied lower than 150 ppm calculated relative to the sulphide ion.

The concentration of the ruthenium on the activated carbon is between0.5 and 5 weight %, and preferably between 1 and 3 weight %.

The higher polyhydric alcohol or mixture of higher polyhydric alcoholsis supplied to the hydrogenation reactor, preferably in an aqueoussolution in a concentration of 20 to 40 weight %.

The higher polyhydric alcohol or mixture of higher polyhydric alcoholsis preferably obtained in a first stage of hydrogenation ofcarbohydrates, carried out at a low basic pH and preferably between 7.5and 8 with a reaction temperature of between 120° and 150° C. This firststage is also preferably carried out in an aqueous solution in thepresence of a basic promoter, such as those previously described, in aquantity sufficient to maintain the pH in the above-described field. Inthis first stage the carbohydrate may consist of monosaccharides ordisaccharides. However the supply preferably consists of an aqueoussolution of glucose which is converted with virtually maximumtheoretical yield into sorbitol. In this hydrogenation stage also, whichis carried out continuously on a fixed bed, the ruthenium catalystsupported on granulated activated carbon, as previously described, isadvantageously used.

The method of preparing the catalyst according to the inventioncomprises the main stages of suspending the granulated activated carbonin water, adding a ruthenium chloride solution to the suspension,adjusting the pH of the suspension to a value of between 4.5 and 8 byadding an alkaline agent, heating the suspension to a temperature ofbetween 70° and 100° C. and maintaining the suspension at thistemperature for a time of between 30 minutes and 2 hours, separating thesolid from the suspension by filtration, re-suspending the solid in asolution of alkaline agent, heating the suspension to a temperature ofbetween 60° and 100° C., bubbling a hydrogen flow into the suspensionfor a time of between 1 and 3 hours, and separating the solid from thesuspension.

The catalyst thus obtained has the features of porosity, specificsurface area and specific weight of the original activated carbon.

Further advantages and features of the method of producing the catalystand of the method according to the invention which uses this catalystwill become apparent from the attached examples, which should not beunderstood as limitations of the scope of the present invention.

EXAMPLE 1

For preparation of the catalyst according to the present invention, anactivated carbon CA 12132 of vegetable origin, and having the followingcharacteristics, was used:

specific surface area: 800 m²/g;

actual specific weight: 2.1 g/cm³;

total volume of the pores: 0.6 cm³/g;

micropore volume (R<75 A): 0.5 cm³/g;

apparent specific weight (bulk density): 0 52 g/cm³;

ash content: 3 weight %;

particle size: 10-18 mesh: (series 2—1 mm): 20-30 weight % 18-35 mesh:(series 1—0.5 mm): 80-70 weight %.

A quantity of 303.3 g of this granulated activated carbon with 6%humidity is suspended in a liter of distilled water and is mechanicallyagitated. After approximately 30 minutes the pH of the suspension is10.5. 2 liters of solution of RuCl₃ containing 15 g of ruthenium isadded slowly to this suspension (over a period of approximately 2 hours)with a constant flow. When this addition is completed, the pH of thesuspension is 0.92. The suspension is adjusted to a pH value of 4.8 bymeans of a 1 molar solution of sodium carbonate and after approximately20 minutes the pH is adjusted to 6 by adding another solution, or sodiumcarbonate. The suspension is then heated to a temperature of 90° C. andis maintained at that temperature for approximately 2 hours. Thegranulated solid is separated from the solution by means of filtering,and is preliminarily washed. It is then resuspended in 2 liters of 0.1molar solution of sodium carbonate. An argon flow is bubbled through thesuspension, which is contained in a three-necked flask and is gentlymechanically agitated, until the air is completely removed. The argonflow is then replaced by a hydrogen flow, and the suspension is heatedto a temperature of 80° C. The suspension is maintained for 2 hours inthe hydrogen flow, preferably at 80° C. The hydrogen flow is thenreplaced by an argon flow and the catalyst is filtered and washed untilthere are no chlorides in the washing waters. The wet ruthenium-basedcatalyst is stored in a closed container.

EXAMPLES 2-3

The catalyst prepared according to example 1 is loaded (100 cm³) into atubular, fixed, regular-flow, trickle-bed reactor provided with agas—fluid separator disposed at the reactor outlet, a tank for supplyingthe reagents and a hydrogen gas tank. The reactor has a diameter of 20.5mm (height of the catalytic bed approximately 30 cm), and is providedwith a coaxial thermocouple which has 3 temperature-measuring areasdisposed at 2.5, 15 and 28 cm below the upper edge of the catalytic bed.On top of the catalytic bed there is a layer of inert material (BerlSaddles) 7.5 cm deep, in order to ensure that the reagents arewell-mixed before coming into contact with the catalytic bed.

The reactor is closed and is connected to the system for supplying thereagents and discharging the products, and is pressurised with nitrogenin order to ensure that it is airtight. The reactor is then supplied atthe test pressure with 2 flows: a mixed hydrogen—water flow, obtained byinjecting water into the hydrogen current in order to saturate it, and asecond flow of deionised water. Before reaching the catalytic bed, thetwo flows are thoroughly mixed through the layer of inert material.Heating of the reactor is then started and the test temperature isreached in approximately 2 hours. In these conditions the water flow isreplaced by a flow of aqueous solution of sorbitol containing sodiumhydroxide and sodium sulphide. After approximately 8 hours thetemperature and spatial velocity (LHSV) of the system are steady. Afterthis period of stabilisation two-hourly collection of the reactionproducts is begun. The fluid samples of the reaction products areanalysed by means of high pressure liquid chromatography (HPLC). The gasoutput by the gas—fluid separator is measured and analysed by means ofgas chromatography, in order to reveal any hydrocarbons present(methane, ethane etc.) and the carbon dioxide. The fluid productcontains mainly 1.2-propylene glycol, ethanediol, butanediol, andsmaller amounts of glycerol, lactic acid and monovalent alcohols, aswell as products such as erythritol, pentanediols, and possiblynon-converted sorbitol. The results of examples 2-3 for two differentreaction temperatures are given in tables 1 and 2 hereinafter, relativerespectively to the operative conditions and distribution of thereaction products.

TABLE 1 Total pres- Temp. S⁼ Sorbitol/NaOH H₂/Sorb. LHSV ConversionExample sure (bar) (° C.) supply (ppm) (molar ratio) (molar ratio) (h⁻¹)(% sorbitol) 2 150 250 600 3 6 1 100 3 150 225 600 3 6 1 100

TABLE 1 Total pres- Temp. S⁼ Sorbitol/NaOH H₂/Sorb. LHSV ConversionExample sure (bar) (° C.) supply (ppm) (molar ratio) (molar ratio) (h⁻¹)(% sorbitol) 2 150 250 600 3 6 1 100 3 150 225 600 3 6 1 100

It can be seen that a decrease in the reaction temperature gives rise toan increase in selectiveness as far as the required reaction productsare concerned.

EXAMPLES 4-8

In these examples the catalyst obtained according to example 1 and thefixed bed reactor described in examples 2-3 are used, at differentspatial velocities (LHSV). The results of these tests are given intables 3 and 4 hereinafter.

TABLE 3 Total pres- Temp. S⁼ Sorbitol/NaOH H₂/Sorb. LHSV ConversionExample sure (bar) (° C.) supply (ppm) (molar ratio) (molar ratio) (h⁻¹)(% sorbitol) 4 150 225 600 3 9 0.67 100 5 150 225 600 3 9 1.00 100 6 150225 600 3 9 1.25 99.8 7 150 225 600 3 9 1.60 99.8 8 150 225 600 3 9 2.5099.0

TABLE 3 Total pres- Temp. S⁼ Sorbitol/NaOH H₂/Sorb. LHSV ConversionExample sure (bar) (° C.) supply (ppm) (molar ratio) (molar ratio) (h⁻¹)(% sorbitol) 4 150 225 600 3 9 0.67 100 5 150 225 600 3 9 1.00 100 6 150225 600 3 9 1.25 99.8 7 150 225 600 3 9 1.60 99.8 8 150 225 600 3 9 2.5099.0

EXAMPLES 9-11

These examples show the effect of the overall reaction pressure on theoutput of diols in the continuous fixed bed process for conversion ofthe sorbitol on a catalyst prepared according to example 1 and used in areactor according to examples 2 and 3. The results of the tests aregiven in tables 5 and 6 hereinafter.

TABLE 5 Total pres- Temp. S⁼ Sorbitol/NaOH H₂/Sorb. LHSV ConversionExample sure (bar) (° C.) supply (ppm) (molar ratio) (molar ratio) (h⁻¹)(% sorbitol)  9 150 225 600 3 6 1.25 99.8 10 105 225 600 3 6 1.25 99.811  75 225 600 3 6 1.25 99.2

TABLE 5 Total pres- Temp. S⁼ Sorbitol/NaOH H₂/Sorb. LHSV ConversionExample sure (bar) (° C.) supply (ppm) (molar ratio) (molar ratio) (h⁻¹)(% sorbitol)  9 150 225 600 3 6 1.25 99.8 10 105 225 600 3 6 1.25 99.811  75 225 600 3 6 1.25 99.2

EXAMPLES 12-15

In these examples the catalyst prepared according to example 1 is usedin a reactor according to examples 2 and 3 in a sorbitol hydrogenolysisprocess which varies the molar ratio between the sorbitol and promoter(NaOH) in the supply flow.

The results are given in tables 7 and 8 hereinafter.

TABLE 7 Total pres- Temp. S⁼ Sorbitol/NaOH H₂/Sorb. LHSV ConversionExample sure (bar) (° C.) supply (ppm) (molar ratio) (molar ratio) (h⁻¹)(% sorbitol) 12 150 235 600  4 6 1.25 100 13 150 235 600  6 6 1.25 99.714 150 235 600 12 6 1.25 74.0 15 150 235 600 30 6 1.25 43.0

TABLE 7 Total pres- Temp. S⁼ Sorbitol/NaOH H₂/Sorb. LHSV ConversionExample sure (bar) (° C.) supply (ppm) (molar ratio) (molar ratio) (h⁻¹)(% sorbitol) 12 150 235 600  4 6 1.25 100 13 150 235 600  6 6 1.25 99.714 150 235 600 12 6 1.25 74.0 15 150 235 600 30 6 1.25 43.0

EXAMPLES 16-18

In these examples the catalyst prepared according to example 1 is usedin a reactor according to examples 2 and 3 for hydrogenation ofsorbitol, varying the sulphur ion content, the sorbitol/promoter molarratio in the supply, and the reaction temperature.

The results are given in tables 9 and 10 hereinafter.

TABLE 9 Total pres- Temp. S⁼ Sorbitol/NaOH H₂/Sorb. LHSV ConversionExample sure (bar) (° C.) supply (ppm) (molar ratio) (molar ratio) (h⁻¹)(% sorbitol) 16 100 225 115 6 6 1.25 78 17 100 225 115 6 6 1.25 76 18100 225  0 3 6 1.25 98.5

TABLE 9 Total pres- Temp. S⁼ Sorbitol/NaOH H₂/Sorb. LHSV ConversionExample sure (bar) (° C.) supply (ppm) (molar ratio) (molar ratio) (h⁻¹)(% sorbitol) 16 100 225 115 6 6 1.25 78 17 100 225 115 6 6 1.25 76 18100 225  0 3 6 1.25 98.5

What is claimed is:
 1. A method of producing a catalyst comprising from0.5 to 5% by weight of ruthenium supported on granulated activatedcarbon useful for hydrogenolysis under pressure of higher polyhydricalcohols, wherein it comprises the steps of: suspending granularactivated carbon in water, the granular activated carbon having: aspecific surface area of from 600 to 1000 m²/g; a total pore volume offrom 0.5 to 1.2 cm³/g; an apparent specific weight (bulk density) offrom 0.45 to 0.55 g/cm³; an actual specific weight of from 1.9 to 2.3g/cm³; a total volume of micropores having a radius smaller than 75 A offrom 0.4 to 0.55 cm³/g; and an ash content of from 2 to 5% by weight;adding an aqueous ruthenium chloride solution to the suspension;adjusting the pH of the suspension to a value of between 4.5 and 8 byadding an alkaline agent; heating the suspension to a temperature ofbetween 70° and 100° C. and maintaining the suspension at thistemperature for a time of between 30 minutes and 2 hours; separating thesolid from the suspension by filtration; re-suspending the solid in asolution of alkaline agent by heating the suspension to a temperature ofbetween 60° and 100° C.; reducing the catalyst obtained by bubbling ahydrogen flow into the suspension for a time of between 1 and 3 hours;and separating the solid from the suspension.
 2. A catalyst according toclaim 1, wherein it has a specific surface area of from 800 to 1000 m²/gand a total pore volume of from 0.6 to 0.7 cm³/g.
 3. A catalyst producedaccording to claim 1, wherein the catalyst has a particle-sizedistribution of 20-30% by weight of granules between 10 and 18 mesh(2.0-1.0 mm) and 80-70% by weight of granules between 18 and 35 mesh(1.0-0.5 mm).
 4. A catalyst produced according to claim
 1. 5. A methodof producing a catalyst comprising from 0.5 to 5% by weight of rutheniumsupported on granulated activated carbon useful for hydrogenolysis underpressure of higher polyhydric alcohols, wherein it comprises the stepsof: (a) suspending granular activated carbon in water, the granularactivated carbon having: a specific surface area of from 600 to 1000m²/g; a total pore volume of from 0.5 to 1.2 cm³/g; an apparent specificweight (bulk density) of from 0.45 to 0.55 g/cm³; an actual specificweight of from 1.9 to 2.3 g/cm³; a total volume of micropores having aradius smaller than 75 A of from 0.4 to 0.55 cm³/g; and an ash contentof from 2 to 5% by weight; (b) adding an aqueous ruthenium chloridesolution to the suspension; (c) adjusting the pH of the suspension to avalue of between 4.5 and 8 by adding an alkaline agent; (d) heating thesuspension to a temperature of between 70° and 100° C. and maintainingthe suspension at this temperature for a time of between 30 minutes and2 hours; (e) separating the solid from the suspension by filtration; (f)re-suspending the solid in a solution of alkaline agent by heating thesuspension to a temperature of between 60° and 100° C.; (g) reducing thecatalyst obtained by bubbling a hydrogen flow into the suspension for atime of between 1 and 3 hours; and (h) separating the solid from thesuspension.
 6. A catalyst produced according to claim
 5. 7. A method ofproducing a catalyst comprising from 1 to 3% by weight of rutheniumsupported on granulated activated carbon, useful for hydrogenolysisunder pressure of higher polyhydric alcohols, wherein it comprises thesteps of: (a) suspending granular activated carbon in water, thegranular activated carbon having: a specific surface area of from 600 to1000 m²/g; a total pore volume of from 0.5 to 1.2 cm³/g; an apparentspecific weight (bulk density) of from 0.45 to 0.55 g/cm³; an actualspecific weight of from 1.9 to 2.3 g/cm³; a total volume of microporeshaving a radius smaller than 75 A of from 0.4 to 0.55 cm³/g; and an ashcontent of from 2 to 5% by weight; (b) adding an aqueous rutheniumchloride solution to the suspension; (c) adjusting the pH of thesuspension to a value of between 4.5 and 8 by adding an alkaline agent;(d) heating the suspension to a temperature of between 70° and 100° C.and maintaining the suspension at this temperature for a time of between30 minutes and 2 hours; (e) separating the solid from the suspension byfiltration; (f) re-suspending the solid in a solution of alkaline agentby heating the suspension to a temperature of between 60° and 100° C.;(g) reducing the catalyst obtained by bubbling a hydrogen flow into thesuspension for a time of between 1 and 3 hours; and (h) separating thesolid from the suspension.
 8. A catalyst produced according to claim 7.9. A catalyst comprising ruthenium in an amount from 0.5 to 5% by weightsupported on active granulated carbon of vegetable origin, the catalystbeing capable of catalyzing hydrogenolysis of higher polyhydric alcoholsunder pressure, the catalyst having: (a) a specific surface area of from600 to 1000 m ² /g; (b) a total pore volume of from 0.5 to 1.2 cm ³ /g;(c) a total volume of micropores having a radius smaller than 75 Å offrom 0.4 to 0.55 cm ³ /g; and (d) an ash content of from 2 to 5 % byweight.
 10. A catalyst according to claim 9, wherein: (a) the specificsurface area is between 800 and 1000 m ² /g; (b) the catalyst has anapparent specific weight (bulk density) of from 0.45 to 0.55 g/cm ³; (c)the catalyst has an actual specific weight of from 1.9 to 2.3 g/cm ³.11. A catalyst according to claim 9, wherein the catalyst has a particlesize distribution of 20-30% by weight of granules between 10 and 18 mesh( 2.0 mm-1.0 mm) and 80 %-70 % by weight of granules between 18 and 35mesh ( 1.0 mm and 0.5 mm).